[mapserver-users] distance between line and a given point usingmapscript

[Mark Brooks]

Steve,

This is a huge help.  The only thing I had not figured out was the 
'toleranceunits' and 'tolerance' fields.  I appreciate your help!

I intend to add many, possible hundreds, lines to a layer.  Then query 
it with a given reference point.  How do I get the number of results and 
then loop through each one?

Best Regards,
Mark


Steve Lime wrote:
>> How do I query a layer with one or more line features to find all
>> features with X miles of a given point?
> 
> Your line layer should like so:
> 
>   LAYER
>     NAME 'lines'
>     TYPE LINE
>     ...other junk...
>     TEMPLATE 'dummy' # to be queryable
>     TOLERANCEUNITS MILES
>     TOLERANCE X
>   END
> 
> Then in mapscript you'd do a 
> 
>   $my_layer->queryByPoint($my_point, MS_MULTIPLE, -1);
> 
> The buffer parameter is used to override a layer tolerance so setting to -1 tells
> the method to ignore it.  If you do use it then it's given in the units of the layer
> being searched (before any projection).
> 
> Does that help?
> 
> Steve
> 
>>>> Mark Brooks <mark_brooks at ncsu.edu> 07/24/09 3:26 PM >>>
> I'm trying to create several new line objects and then find the lines
> that are within x miles of a given point.  (i.e., how far away a given
> point is from the track of a hurricane or the path of a ship).  I'm
> having some difficulties and I hope someone can help.
> 
> How do I query a layer with one or more line features to find all 
> features with X miles of a given point?
> 
> Here is how I'm approaching the problem in PHP:
> 
> // Test array of points.  This is used to make a line.
> $points[0]['lat'] = 35.5;
> $points[0]['lon'] = -78.8;
> $points[1]['lat'] = 36.5;
> $points[1]['lon'] = -79.8;
> $points[2]['lat'] = 37.5;
> $points[2]['lon'] = -80.1;
> 
> // make new map object.
> $map = ms_newMapObj('mapdata/mymap.map');
> 
> // Create new line
> $my_line = ms_newLineObj();
> 
> // Loop through points, and add to the line
> while (list(,$coordinate)=each($points)){
> 
>          // Create new point object
>          $my_point = ms_newpointObj();
>          $my_point->setXY($coordinate['lon'],$coordinate['lat']);
> 
>          // Add point to line object
>          $my_line->add($my_point);
> }
> 
> // Now create a new shape
> $my_shape = ms_newShapeObj(MS_SHAPE_LINE);
> $my_shape->add($my_line);
> 
> // create new layer
> $my_layer = ms_newLayerObj($map);
> 
> // set some fields for this new layer
> //$my_layer->set("units","miles");  // does not seem to work as expected
> 
> // Create new class and add TEMPLATE.  This is required for queries on 
> the layer to work?
> $my_class = ms_newClassObj($my_layer);
> $my_class->set("template",'/home/www/html/query_template.html');
> 
> // Add feature to the layer
> $my_layer->addFeature($my_shape);
> 
> // Draw map. Query doesn't work if I don't do this now.
> $map->draw();
> 
> // Make a new point object that will be our ref point
> // to check how far away the line is from this point.
> $my_point = ms_newpointObj();
> $my_point->setXY(-82,36); // lon, lat
> 
> // Run a point query on the line object layer; layer must have a class 
> with a LAYER TEMPLATE value
> // The third argument is the buffer tolerance.  Default unit is pixels? 
>   Must figure out how to make miles or km.
> if ($my_layer->queryByPoint($my_point,MS_SINGLE,1)==MS_SUCCESS){
> 
>          $my_result = $my_layer->getResult(0);  // Get the result
>          $my_layer = 
> $my_layer->getShape($my_result->tileindex,$my_result->shapeindex);  // 
> Get the shape
> 
> }
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> 


-- 

    Mark Brooks
    State Climate Office of North Carolina
    Box 7236, NC State University
    Raleigh, NC 27695-7236

    Phone:  919.515.1446
    Fax:  919.515.1441